1. Technical Field
The invention relates to a projection lens device for magnifying and projecting display information and the like from a light valve such as a transmissive or reflective liquid crystal display device or a DMD (a digital micro mirror device), and in particular, relates to a projection lens device suitable for a rear projection display apparatus such as rear projection televisions, and a projection display apparatus using the projection lens device.
2. Description of the Related Art
Known projection display apparatuses include (i) a front projection display apparatus in which a projection lens device is arranged on the same side as a viewer, the front projection display apparatus that forms an image of light beams exiting from the projection lens device on a reflective display screen, and (ii) a rear projection display apparatus in which a projection lens device is arranged across a display screen from a viewer, the rear projection display apparatus that forms an image of light beams exiting from the projection lens device on the transmissive display screen.
As to the rear projection display apparatus, the following configuration is known like, for example, a rear projection television. That is, various components from a light source to a screen are housed in a cabinet, and light beams containing image information from a projection lens device disposed on a rear side thereof are projected toward the screen disposed in front of the cabinet.
Recently, various projection lens devices for use in the cabinet-type projection display apparatus have been proposed.
A projection lens device is demanded to allow for projection of a large-size image with a short projection distance. Particularly, a projection lens device for the rear projection is demanded to achieve a wider angle of view because a decrease in thickness of the display apparatus is strongly demanded.
Also, a large back focal length is demanded in order to provide a synthesizing section for synthesizing light beams from respective light valves in an optical system that uses the plurality of light valves for colorization, to separate illumination light beams and projection light beams, and to solve problems caused by heat.
In response to these demands, lenses having a relatively-long back focal length and an angle of view, on a magnification side, of 100 degrees or more have been described in JP 2003-15033 A (corresponding to U.S. Pat. No. 6,624,952), JP 2004-326079 A (U.S. Pat. Nos. 6,947,222), 7,123,426, and 7,126,767.
In a projection display apparatus, particularly in a rear projection type device, for the purpose of deflecting an optical path in a predetermined position in order to downsize the display apparatus, it is considered that inserting a reflective element into the projection lens device is advantageous.
However, U.S. Pat. Nos. 7,123,426, and 7,126,767 fail to have a concept of inserting a reflective element into an optical path. Also, in order to compensate for a narrow space, JP 2003-15033 A and JP 2004-326079 A uses a prism for lengthening an optical path, in stead of a reflection mirror, as a reflective element inserted into the optical path, which increases a manufacturing cost.